The present invention relates generally to the field of wastewater treatment and, more particularly, to dealing with odors emitted by organic waste.
Over the past decades there has been a shift from smaller localized family farms toward larger integrated confinement agricultural operations. Large agricultural operations typically utilize confinement barns to house a large number of livestock such as swine. It is not uncommon for hog-confinement operations to be grouped in close proximity, forming xe2x80x9cmega-farmsxe2x80x9d which may house tens of thousands of hogs. While these larger agricultural operations have numerous advantages, they also encounter significant pollution problems arising from the handling and treatment of manure and wastewater. Pollution problems associated with liquid animal waste include nitrogen, phosphorus, solids, bacteria and foul odors that result from anaerobic digestion. Environmental concerns more specifically center on odor and water quality issues.
Currently, for treatment of animal wastes and wastewater most agricultural facilities use anaerobic digestion, i.e. anaerobic bacteria consume some or much of the organic waste. The primary reason for using anaerobic digestion is that it is natural but it also has the advantages of simplicity and low cost. Wastewater is simply discharged from the animal storage facility into one or more open lagoons where the waste undergoes natural anaerobic digestion. However, noxious gases including ammonia, methane, hydrogen sulfide, fatty acids, and indoles may be emitted from anaerobic lagoons at hog farms as well as within the animal storage facilities. Additionally, the time required for complete digestion of the organic wastes is relatively long, typically lasting from weeks to months. Some current regulations require a residence time of 180 days for animal waste facilities using anaerobic lagoons for digestion. Odors emanating from lagoons, confinement houses, and fields onto which wastes are sprayed create a nuisance. In fact, as a result of odor problems associated with anaerobic lagoons, some states have legally mandated buffer zones or designated land areas between lagoon sites and populated areas. In addition, the noxious gases produced by animal waste create a potentially hazardous environment in animal storage facilities for humans working in such facilities and the animals housed in these facilities.
Hog lagoon liquid effluent characteristically has high levels of nitrogen and phosphorus that cannot be decreased to acceptable levels by anaerobic treatment alone. Even with bacterial digestion, significant amounts of sludge accumulate in an anaerobic lagoon. Anaerobic lagoons may fill to capacity fairly quickly which displaces the designed retention capacity of the lagoon fairly quickly and often serve to provide only partial pretreatment. Often, anaerobic settling lagoons serve to separate solids and reduce or decompose wastes enough to land spread or spray the waste on irrigation fields.
Continuing efforts are being made to improve agricultural and animal waste treatment methods and apparatus. For example, one process known in the art is the transformation of animal waste wherein solids are precipitated in a solids reactor, the treated slurry is passed to a bioreactor zone where soluble phosphorus is precipitated with metallic salts, the slurry is aerobically and anaerobically treated to form an active biomass. The aqueous slurry containing bio-converted phosphorus is passed into a polishing eco-reactor zone wherein at least a portion of the slurry is converted to a beneficial humus material. However, in operation, the system requires numerous chemical feeds and a series of wetland cells comprising microorganisms, animals and plants.
Several studies done in the past several years have also addressed the issue of reducing odors by covering manure storage units. For example, many types of natural floating covers formed by fibrous materials have been used to reduce manure odor. Artificial floating crusts have consisted of chopped straw, plastic foam pellets, a combination of straw and pellets, mats, or tarpaulins. Tight covers have included plastic covers sealed at the edge and light constructed roofs. These types of covers have proven to be inadequate for several reasons. Such covers have not sufficiently eliminated odorous emissions. Also, such covers cannot be efficiently utilized in an animal storage facility, where the pit must remain open to receive waste as it is generated by the housed animals. Natural floating covers have also been known to fail under conditions such as rainy weather, which causes the floating crusts to become submerged in the waste.
The present invention provides a method and apparatus for treatment of agricultural animal waste to minimize odorous emissions. The treatment includes a layer of oil, preferably vegetable oil, and activated carbon applied to the surface of liquid animal waste. The ratio of oil to activated carbon is preferably approximately 5:1. This layer of treatment creates a seal that inhibits the emission of odorous gases. Even when exposed to rain, the oil/activated carbon layer keeps the liquid waste odors sealed.
The treatment also includes the injection of a base buffering agent into the liquid waste, below the oil/activated carbon layer. This base buffering agent neutralizes the acidic liquid animal waste, thereby minimizing the odorous gases, emitted from the liquid waste. The addition of the base buffering agent is controlled to prevent the occurrence of an excessively high pH level in the waste. This is necessary to maintain the anaerobic environment within the treated waste, which is required for the treatment to work.
The present invention includes an applicator system for applying the treatment to the liquid animal waste without agitating the waste beneath the surface oil/activated carbon layer. This is necessary because agitation of the waste beneath the surface causes gases and odors to be emitted.
The present invention also includes a retainer system which prevents the treatment from being pumped away with the liquid waste during emptying of a treated animal waste pit. This system is advantageous to the extent that it allows the treatment to be retained after pumping away the liquid waste, thereby obviating the need to apply a new treatment after each emptying of the waste pit.
The present invention provides many advantages, including reducing emission of odorous gases, stopping the evaporation of liquids beneath the surface of the treatment to reduce the humidity levels in animal storage facilities, maintaining higher quality of air in animal storage facilities, liquefying waste solids through bacterial activity and the establishment of an anaerobic environment, maintaining the seal above the liquid waste because any of the treatment dragged below the surface by waste falling on the treatment surface layer automatically reemerges at the surface, improving feed quality as moisture and airborne bacteria growth is reduced, reducing harmful dust particles in the animal waste environment, stopping erosion in lagoons by inhibiting agitation of the liquid waste, and reducing airborne bacteria which causes and spreads infectious diseases.